Stacked Soil Amendments & Amelioration Methods - Technical Project Update

By Kate Parker, WMG Project Officer

Background

In the West Midlands region, the soils present a unique set of challenges for farmers, with issues such as soil water repellence, nutrient leaching, and low nutrient levels. These difficulties are largely due to the low percentage of clay and organic carbon, resulting in poor holding capacity for nutrients, moisture, and soil structure.

As a response, farmers are increasingly turning their attention towards enhancing soil fertility using the next generation of soil amelioration tools and organic amendment options. The aim is to address the low soil carbon levels and improve the overall health and resilience of the soil, particularly on the sandy soils of the West Midlands region.

A significant trial is underway to assess the efficacy of various organic amendment options in increasing soil organic matter. Unlike previous studies that assessed these methods individually, this trial is focused on exploring combinations of amendments and amelioration methods to identify potential synergistic benefits for long-term improvements in soil carbon levels, health, and crop grain yield.

This trial is exploring if the stacking of soil amendments and amelioration strategies can result in synergistic benefits that improve soil health and crop production. This report outlines the impact of a range of soil management strategies on the growth of serradella and nutrient uptake in the third year of the trial.

Results

Start of Flowering Biomass

Serradella biomass production has been significantly higher in 2024 (year-to-date) as January to August rainfall was significantly higher than the total rainfall received in 2023 (Table 2). The increase in biomass production in 2024 across all treatments compared to 2023 is also likely impacted by the increased density of serradella seedlings as the site is a regenerating pasture (data not presented). There was no significant difference between 2021 or 2022 amendments treatments in 2024 (4 and 3 years following treatments, respectively). For the 2021 amelioration treatments, both rotary spading and mouldboard ploughing had a positive impact on serradella biomass production by the time of sampling in August, 8 weeks after the season break on the 1^st June 2024.

Anthesis biomass:

Anthesis biomass was increased by the use of soil amelioration (rotary spading, mouldboarding) compared to the untreated control, while the addition of compost had no effect (Figure 4). Interestingly, Ironman Gypsum recorded significantly lower biomass than the untreated control (NIL) in 2021 Amendments. There was also significant difference between 2022 Amendment plots with Biochar/Frass recording higher biomass than NIL treatments, however, there was no significant interactions found between treatments for any biomass measurements undertaken (flowering or anthesis timing). There was a greater difference in the biomass at anthesis compared to the start of flowering which indicates that the timing of benefit of various amendments can be different during the season. There were no synergies identified between the amelioration and amendment treatments, only additive effects.

Nutrient uptake

Nutrient analysis was conducted on the anthesis biomass samples and overall, there was an increase in nitrogen (N), phosphorus (P), potassium (K), and sulphur (S) for both mouldboard and rotary spading compared to the untreated control (Figure 5). The addition of Biochar/Frass also increased the amount of N,P, and K taken up in the plant but did not impact the total S taken up and is consistent with pre-application testing showing biochar with relatively low levels of sulfur (Yeap 2021). In the 2021 amendments, there was a trend for the compost and NIL treatments to be higher than ironman gypsum except in sulphur and total nitrogen. As Ironman gypsum has high levels of sulphur in its composition along with a high PBI (Yeap 2021), these were expected to significantly impact Phosphorus and Sulphur (R Bell, pers comm). Within the 2021 amendments, the compost and NIL treatments show no significant differences between each other, this suggests that any effect compost may have had on nutrient uptake when it was applied 3 years ago, have since worn off.

Summary

This trial aimed to explore the interactive and synergistic effects of stacking soil amelioration and amendments together to increase crop and pasture production. While there have been significant increases in biomass and nutrient uptake in serradella in the 2024 year (3-4 years following amendment and ameliorant application) there appears to be no interactions present between any of the treatments. Instead, there is strong evidence of additive effects on plant growth for most soil health strategies being implemented. The practical implication for farmers is that soil amelioration and use of Biochar/Frass are effective ways of increasing crop growth that can be both used separately or together to increase plant production.

The addition of compost, while it has not been significant, has trended over the last 4 years towards having a positive benefit to crop production. In 2024, this benefit seems to have faded as there was no benefit to the application of compost for biomass or nutrient uptake. This has implications for the use of compost by farmers to improve crop production as re-application may be required every 3-4 years to sustain the benefits of this organic amendment. This study is limited in its assessment of the rate of compost applied and type/nutrient analysis of the compost, which are both expected to impact the size and longevity of response.

The use of Ironman Gypsum, a byproduct from the mining industry, is considered a novel but potentially effective soil amendment to retain organic matter and nutrients in the root zone of sandy soil types. The iron oxide in Ironman Gypsum can increase the retention of organic matter in the soil and may impact nitrogen availability, however, this may be a short term impact. Ironman Gypsum releases soluble calcium, which may inhibit potassium uptake while increasing sulfur uptake and this was evident in the results of this trial in 2024. It also contains significant amounts of iron oxide, which may account for the lower phosphate uptake due to the adsorption of phosphorus to iron in the soil, and this could be a beneficial trait in the long term to prevent leaching if it does not have a significant short term impact on plant growth. Further work is needed to understand the short and long term impacts of Ironman Gypsum on plant growth in the region, including whether the benefit of using this product is dependent on varying the fertiliser inputs on soils where Ironman Gypsum has been used to negate the short term impacts of this product.

This trial site will continue to assess the growth of crops on this deep sandy soil which is characteristic of the region and is commonly associated with poor nutrient and water holding capacity, nutrient leaching, soil water repellence, low nutrient levels, and compaction. Mitigating the effect of these constraints using soil amelioration practices has been previously shown to have a positive impact soil health and crop profitability. As we further understand the role and application of organic amendments, farmers in the region can take advantage of the many sources now available. While there has been few synergistic benefits between treatments, there are significant additive effects that mean we can build the health of our soils stepwise over time.

This project is supported by the Western Australian Carbon Farming and Land Restoration Program, The CRC for High Performance Soils, and Future Green Solutions.